CN116940714A

CN116940714A - Method for producing an enamelled steel part, enamelled steel part and use thereof

Info

Publication number: CN116940714A
Application number: CN202280017362.4A
Authority: CN
Inventors: P·夏勒
Original assignee: BSH Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2021-02-26
Filing date: 2022-02-15
Publication date: 2023-10-24
Also published as: US20240124983A1; EP4298267A1; WO2022179884A1; DE102021201881A1

Abstract

The invention relates to a method for manufacturing an enamelled steel part, comprising the steps of: providing a steel component; coating a steel component with an adhesion promoter layer comprising at least one adhesion metal, adhesion metal oxide or salt thereof and a binder; and enamelling the coated steel part. The invention also relates to an enamelled steel part obtainable with the method. The invention also relates to the use of the enamelled steel part.

Description

Method for producing an enamelled steel part, enamelled steel part and use thereof

The present invention relates to a method of manufacturing an enamelled steel part and an enamelled steel part obtainable with the method.

Prior Art

Enamelled steel parts and methods for manufacturing enamelled steel parts have long been known. A key factor here is to ensure adequate adhesion of the steel substrate to the enamel. It is well known that at the interface between steel and enamel there are various metal oxides that improve adhesion, such as nickel oxide. In the prior art, the following techniques are used in particular to form a sufficient adhesion of the enamel to the steel substrate.

First, a method of manufacturing an enamelled steel part is known, wherein a metal substrate is applied to improve adhesion before the application of the enamel layer. A corresponding method is disclosed, for example, in CH 409573. Here, the base layer is electrochemically deposited using an electroplating process. In a subsequent enamelling process, the metallic base layer is at least partially converted into an oxide layer, which increases the adhesion of the enamel to the steel substrate. However, electroplating processes are associated with high energy and equipment costs and are very detrimental to the environment and health. Furthermore, the adhesion of enamel to certain types of steel may be insufficient.

Secondly, it is known to apply a plurality of enamel layers therein, wherein at least a metal oxide is added to the first enamel layer, which increases the adhesion to the substrate. The disadvantage of these conventional methods is that a plurality of enamelling steps are required, which is disadvantageous from a cost and process technology point of view. Furthermore, the application of enamel powders with metal oxides that increase adhesion is very difficult, as they are harmful to health and the environment.

Third, a single layer direct enamelling process is known, wherein only a single enamel layer is applied to the substrate surface. Metal oxide is added to the enamel layer, which increases adhesion. However, these methods have the disadvantage that the metal oxide is present not only in the boundary layer but also in the entire enamel layer, so that a relatively large amount of metal oxide is required to ensure adequate adhesion. The presence of metal oxides on enamel surfaces also leads to other disadvantages such as lower chemical and mechanical stability, e.g. resistance to chemicals, water or vapour, corrosion resistance, scratch resistance or cleanability. Furthermore, the use of such enamelled steel parts may be limited, especially in food contact applications, because of the potentially harmful health of the metal oxides present on the enamel surface.

For these reasons, the methods of manufacturing enamelled steel products known in the prior art can be improved.

Object of the Invention

The object of the present invention is to provide a method for manufacturing an enamelled steel part which method gives the drawbacks associated with the prior art. In particular, it is an object to provide a method which achieves excellent adhesion of enamel to a steel substrate even with a small total amount of adhesion metal and which can use various types of steel as a substrate. Another object of the method is to reduce energy and equipment costs, as well as environmental and health hazards. Another object is to provide a method of manufacturing an enamelled steel part which has excellent chemical and mechanical stability, such as resistance to chemicals, water or vapour, corrosion resistance, scratch resistance or cleanability, and is suitable for food contact applications without limitation.

It is a further object of the present invention to provide an enamelled steel part with corresponding properties. In particular, it is an object to provide an enamelled steel part which has excellent adhesion of enamel to a steel substrate even in the case of a small total amount of adhesion metal and which can use various types of steel as a substrate. Another object is to provide an enamelled steel part with excellent chemical and mechanical stability, such as resistance to chemicals, water or vapour, corrosion resistance, scratch resistance and cleanability. Another object is to provide an enamelled steel part which is suitable for a variety of uses, in particular for food contact areas.

Brief description of the invention

This object is achieved by a method according to claim 1. Preferred embodiments of the method are defined in the dependent claims 2 to 13, which are also included in combination with each other. This object is also achieved by an enamelled steel part according to claim 14. This object is also achieved by the use of an enamelled steel part according to claim 15.

Detailed Description

The invention relates to a method for manufacturing an enamelled steel part, comprising the steps of: providing a steel component; coating a steel component with an adhesion promoter layer comprising at least one adhesion metal, adhesion metal oxide or salt thereof and a binder; and enamelling the coated steel part.

The shape and type of the steel part or steel substrate is not limited. In particular, flat components, such as metal plates, plates or films, can be used, but also components having a three-dimensional geometry, such as deep drawn or cast molded parts, can be used. All types of steel may be used, for example alloyed or unalloyed types of steel, for example IF or EK steel (see EN10209, for example DC0 xEK) steel. According to the invention, the layer deposition is performed on the finished steel part, i.e. the resulting enamelled steel part is no longer deformed.

This method is of particular importance for the present invention in the step of coating the steel component with a specific adhesion promoter layer prior to enamelling. The adhesion promoter layer according to the present invention comprises at least one adhesion metal, adhesion metal oxide or salt thereof and a binder. The adhesion promoter layer serves as a primer and is also referred to as a sacrificial layer, since it is at least partially dissolved in an embodiment in a subsequent enamelling process. The presence of the binder and the adhesion metal, adhesion metal oxide or salt thereof in the adhesion promoter layer is necessary to achieve the advantages of the invention described in detail below.

The adhesion metal may be used in elemental form, as an oxide or as a salt thereof. If the adhesion metal is not present as an oxide, it is oxidized in a subsequent enamelling process. The resulting adhesion oxide ensures excellent adhesion of the enamel to the steel substrate.

In an embodiment, the resulting adherent metal oxide may at least partially diffuse into the enamel layer. Thus, in an embodiment, a concentration gradient of the adhering metal oxide occurs in the resulting enamel layer such that the concentration of adhering metal is greatest at the interface with the steel substrate and decreases towards the surface. According to the invention, there is no adhering metal oxide at the surface of the enamel layer. REM/EXD can be used to detect the distribution of adherent metal oxide in the enamel layer.

The binder ensures a uniform distribution of the adhesion metal, adhesion metal oxide or salt thereof in the adhesion promoter layer. The presence of the adhesive also ensures that the adhesion promoter layer can be applied easily and uniformly. The binder is configured such that it does not interfere with the enamelling process and in embodiments it thermally decomposes and/or bonds with the enamel layer in a subsequent enamelling step.

By the method according to the invention it is further ensured that the adhesion metal, adhesion metal oxide or salt thereof contained in the adhesion promoter layer is not present at the surface of the enamelled steel part, but only at the boundary layer between the steel substrate and the enamel. This in turn results in an improvement of the chemical and mechanical stability of the coating, in particular of the water, steam, food and corrosion stability, compared to the conventional direct enamelling process. By having no adhering metal at the surface, which is a risk for health and the environment, it is further ensured that the enamelled steel part is suitable for use in food-contact applications without limitation.

With respect to this method, it is also advantageous to avoid depositing the adherent metal by a chemical or electrochemical process, which is disadvantageous from a cost and environmental point of view. Furthermore, enamelling can be carried out using enamel powders which do not contain adhesion metal components, which are very expensive and present a risk to the environment and health. At the same time, the method according to the invention has the advantage over the conventional direct enameling method that a smaller amount of adhering metal can be used, but at the same time excellent adhesion is achieved, i.e. the method according to the invention is advantageous from a cost point of view as well as from an environmental and health point of view.

Improved enamel adhesion can be achieved despite the use of a smaller amount of adhesion metal. Furthermore, by better enamel adherence, cheaper and better usable types of steel (e.g. IF instead of ED) can be used. The application of the adhesion promoter layer can be generally easier and less risky and less energy consuming than conventional processes.

In a preferred embodiment, the adhesion promoter layer is a sol-gel based system, i.e. may be selected from a variety of coating methods suitable for sol-gel materials, such as dip coating, flow coating or spray coating. The adhesion promoter layer can thus be applied uniformly, effectively, inexpensively and with a small layer thickness. Furthermore, an excellent adhesion of the enamel to the steel substrate can thereby be achieved. Sol-gel based systems are known in the art. To produce the layer, a sol serving as a coating solution is first applied to the substrate surface. During the coating process and the sol drying process, the precursors used undergo hydrolysis and condensation reactions until the sol particles aggregate to form a solid gel film. The precursor comprises a reactant material for forming the layer, in particular a reactant material for forming the binder. Suitable precursors are known and are not limited in accordance with the invention.

The type of the adhesion metal is not limited. One, two or more of the adhesion metals, adhesion metal oxides or salts thereof may be used, i.e., the adhesion metals may be used in either elemental form or cationic form. In a preferred embodiment, the adhesion metal is selected from nickel, cobalt, copper, tin, iron, molybdenum or arsenic, preferably nickel, copper, iron or molybdenum. The use of these adhesion metals results in a particularly good adhesion of the enamel layer to the steel substrate. If the adhesion metal is used in elemental form, oxidation occurs in an embodiment in a subsequent enamelling to produce an adhesion metal oxide. The type of oxide is not limited. All kinds of oxides or salts thereof may be used. Preferred inorganic salts are, for example, silicates, aluminates or halides, such as chlorides. In an alternative embodiment, organic anions, such as polymeric organic anions, may be used. It is particularly preferred that the adhesion metal has been used as an oxide, i.e. that the elemental adhesion metal does not have to be oxidized, as is necessary for example in conventional methods with a metallic substrate layer. The method according to the invention thus has the advantage of greater flexibility with respect to the traditional method of manufacturing enamelled steel parts, in which the metal substrate is applied before the enamel layer is applied, for example in terms of the type of adhesion metal and enamel that can be used.

The concentration of the adhesion metal or salt thereof in the adhesion promoter layer is not limited. Suitable concentrations of the adhesion metal or salt thereof are, for example, from 1 to 95% by weight, preferably from 20 to 90% by weight, more preferably from 40 to 80% by weight, more preferably from 50 to 70% by weight, based on the total weight of the adhesion promoter.

The type of adhesive is not limited. One, two or more different binders may be used. The adhesive is the main component of the adhesion promoter, i.e. the matrix, upon application. The adhesive ensures good applicability and uniform distribution of the adhesion metal or its salt in the adhesion promoter layer. The main task is as follows: the adhesion promoter layer is fixed to the component until enamelled.

In embodiments, the binder is an inorganic binder. The inorganic binder is preferably formed by a sol-gel process (sol-gel is partially organic). The advantage of inorganic binders is that the adhesion promoter layer has good compatibility with the enamel layer which is usually composed of silicate-or oxide-based systems. Particularly good adhesion can thus be achieved. Furthermore, in particular, good compatibility with adhesion metals, in particular adhesion metal oxides, is achieved.

The type of the inorganic binder is not limited. The inorganic binder is preferably an oxide-based binder, which is particularly preferably selected from the group consisting of an alumina-based binder, a titania-based binder or a silicate-based binder. Adhesives of this type are generally known and will not be explained further here. The advantage of these systems is that they are readily and inexpensively available and compatible with common enamel layers. Furthermore, the adhesion promoter system can thus be varied and easily adjusted and also give rise to excellent adhesion. It is also highly compatible with a large amount of adhesion metal or adhesion metal oxide.

In an alternative embodiment, the binder is an organic binder. The type of organic binder is not limited. However, in this case, for the subsequent enamelling process, the organic binder must thermally decompose during the enamelling step. The adhesive is preferably a polymer-based adhesive. Organic binders, in particular polymeric organic binders, can be obtained and applied easily and inexpensively.

Preferably, the polymer-based adhesive is selected from epoxide-based adhesives, acrylate-based adhesives such as poly (meth) acrylate adhesives, polyester-based adhesives, polyurethane-based adhesives, polycarbonate-based adhesives, rubber-based adhesives such as gum arabic adhesives, or combinations thereof. These binders can be easily and completely thermally decomposed, thus leading to particularly advantageous adhesion properties of the resulting enamelled steel part. It is also highly compatible with a large amount of adhesion metal or adhesion metal oxide. In embodiments, the organic binder is a polymeric anionic binder. This has the advantage of being useful for making an adhesion promoter system with a high proportion of adhering metal cations that can be easily applied.

All other types of binder systems, such as organic-inorganic hybrid systems, are also included according to the present invention. Furthermore, in some embodiments, inorganic particles such as silica, alumina, titania, or zirconia particles may be added to the binder. In particular, adhesive systems comprising nanoparticles are included, which lead to particularly good adhesion properties.

In embodiments, the adhesion promoter comprises other components or additives, such as fillers, compatibilizers, stabilizers, dyes, antioxidants, thixotropic agents, and the like. These are generally known and will not be explained further here. In embodiments, the total amount of the other components or additives is 10 wt% or less, preferably 1 wt% to 0.001 wt%, more preferably 0.1 wt% to 0.01 wt%, based on the total weight of the adhesion promoter.

According to the present invention, the type of application of the adhesion promoter layer is not limited. All conventional coating processes can be used.

In embodiments, the coating is performed by a wet coating process. The adhesion promoter is applied here in liquid form, for example as a solution, dispersion, suspension or emulsion. The concentration of the adhesion promoter is not limited and is, for example, 1 to 90% by weight, preferably 10 to 70% by weight, more preferably 20 to 50% by weight. According to the present invention, the type of wet coating process is not limited. Suitable wet coating processes are known in the art. The application is preferably carried out by dip coating, spray coating or spray coating processes. However, all other common methods of application are also included according to the invention. The wet coating process allows for a uniform, efficient and inexpensive application of the adhesion promoter layer.

In particular, in wet coating processes, the adhesion promoter is present in the form of an aqueous solution, wherein the solvent comprises water. However, the type of solvent may vary. In particular, according to the invention solvent mixtures are included, for example mixtures of water and alcohols, for example ethanol, isopropanol or tert-butanol. The mixing ratio is not limited, and is, for example, 90:10 to 10:90, preferably 80:40 to 20:80, more preferably 60:40 to 40:60 (Water: alcohol). A particularly inexpensive, efficient and environmentally friendly application can thus be achieved. Similarly, the adhesion promoter may be present in the form of an aqueous dispersion, suspension or emulsion.

If the adhesion promoter layer is applied by a wet coating process, the method preferably further comprises the step of drying the coated component prior to enamelling. The drying may be carried out at a temperature of, for example, above 21 ℃ at room temperature, for example, 30 to 200 ℃, preferably 50 to 100 ℃. Drying can be carried out, for example, with IR radiation or with hot air. This allows for an inexpensive and fast process management, wherein in particular steel parts with complex three-dimensional geometries (e.g. with back-cuts) can be well coated.

In a particularly preferred embodiment of the wet coating, the coating is carried out in commercial large-scale dip or spray equipment. The method is carried out in such a way that, after washing and optionally pretreatment of the steel substrate, an adhesion promoter layer is applied in the rinse bath of the existing washing apparatus. Subsequently, drying is carried out in the drying phase of the enamelling washing apparatus and an enamel layer is applied. This has the advantage that the drying stage of the washing apparatus can be used to dry the adhesion promoter layer and that no additional drying is required after application of the adhesion promoter layer. This embodiment of the method is therefore particularly advantageous from an energy point of view.

As an alternative to the wet coating process, in embodiments, the coating may be performed by a powder coating process. Suitable process conditions for powder coating are generally known and are not limiting according to the invention. The advantage of applying the coating in powder form is that it can be applied very efficiently, at low cost and with little outlay on equipment. In particular, the drying step necessary in the wet coating process is omitted in powder coating.

In a preferred embodiment, the method further comprises the step of cleaning the steel part prior to coating. Suitable cleaning processes are not limited in accordance with the present invention. However, the cleaning step is preferably selected from washing, annealing, degreasing, pickling or a combination thereof. In this way, particularly effective and valuable cleaning of the feces is possible.

The substrate surface may also be roughened mechanically, for example by a sand blasting process using glass particles or corundum, or otherwise chemically or physically treated to achieve improved adhesion prior to application of the adhesion promoter. Alternatives to mechanical roughening are, for example, pickling, etching, evaporation, etching or milling. Furthermore, the substrate to be coated is optionally cleaned by immersing the substrate in a cleaning bath filled with, for example, a conventional detergent solution, to remove dirt and fat residues. Optionally, the process may be assisted by the application of ultrasound.

The layer thickness of the resulting adhesion promoter layer is not limited according to the invention. In embodiments, the adhesion promoter layer is applied in a layer thickness of 25 μm or less, preferably 0.01 to 20 μm, more preferably 0.05 to 15 μm, still more preferably 0.1 to 10 μm. Excellent adhesion can thereby be achieved in combination with efficient and inexpensive process management. The layer thickness of the adhesion promoter layer was measured using white light interferometry or X-ray fluorescence.

Enamelling processes for applying enamel layers, such as process conditions and reactant compositions and enamel compositions, are generally known and will not be further explained herein. In the context of the present invention, enamels are materials having an inorganic composition, generally based on silicates and oxides, which are produced in the form of a generally glassy solidification by melting, sintering or sintering (which means a melting process which is interrupted shortly before melting together). Such materials (sometimes with additives) are usually applied to the carrier material in the form of one or more layers and melt at high temperatures and short combustion times, with the aim of usually coating the carrier material.

The thickness of the layer of the enamel layer obtained is not limited according to the invention. In an embodiment, the enamel layer is applied in a layer thickness of 1mm or less, preferably 1 to 500 μm, more preferably 5 to 250 μm, still more preferably 10 to 180 μm. Thus, particularly good chemical and mechanical properties of the enamel, excellent adhesion to the substrate, can be achieved in combination with an efficient and inexpensive process management. The layer thickness of the enamel layer was measured microscopically on a cross-sectional plate.

The invention also comprises an enamelled steel part obtainable by the above method. The steel part of the present invention is structurally different from the enamelled steel part manufactured by the above-described conventional method. The enamelled steel part according to the invention thus has an improved adhesion of enamel to the steel substrate even in the case of a low total amount of adhering metal. Thus, various types of steel may be used as the substrate. Furthermore, enamelled steel parts have excellent chemical and mechanical stability, such as resistance to chemicals, water or steam, corrosion resistance, scratch resistance or cleanability. Enamelled steel parts are also suitable for a large number of applications, in particular for food contact areas.

The enamelled steel part according to the invention is suitable for a large number of applications. In particular, the enamelled steel part can be used in kitchen appliances, preferably ovens, in particular as a baking tube, baking tray or mould, and as an accessory in or on a cooking chamber, such as a hot air guide, a grill grid, a baking oven stem, a baking tray receiving grid, a telescopic guide, a steam bar and/or an air discharge plate.

Claims

1. A method of manufacturing an enamelled steel part comprising the steps of:

providing a steel component;

coating a steel component with an adhesion promoter layer comprising at least one adhesion metal or adhesion metal oxide or salt thereof and a binder;

enamelling the coated steel part.

2. The method of claim 1, wherein the adhesion promoter layer is a sol-gel based system.

3. The method according to claim 1 or 2, wherein the adhesion metal is selected from nickel, cobalt, copper, tin, iron, molybdenum or arsenic, preferably nickel, copper, iron or molybdenum, and wherein the adhesion metal is preferably used as an oxide, in elemental form or as a salt thereof.

4. A method according to any one of claims 1 to 3, wherein the binder is an inorganic binder.

5. The method of claim 4, wherein the inorganic binder is an oxide-based binder, preferably selected from an alumina-based binder, a titania-based binder, or a silicate-based binder.

6. The method according to any one of claims 1 to 5, wherein the binder is an organic binder which thermally decomposes in the enamelling step, wherein the binder is preferably a polymer-based binder.

7. The method of claim 6, wherein the polymer-based adhesive is selected from an epoxide-based adhesive, an acrylate-based adhesive such as a poly (meth) acrylate adhesive, a polyester-based adhesive, a polyurethane-based adhesive, a polycarbonate-based adhesive, a rubber-based adhesive such as a gum arabic adhesive, or a combination thereof.

8. The method according to any one of claims 1 to 7, wherein the coating is performed by a wet coating process, preferably by dip coating, spray coating or spray coating, wherein the solvent preferably comprises water.

9. The method of claim 8, further comprising the step of drying the coated component prior to enamelling.

10. The method according to any one of claims 1 to 7, wherein the coating is performed by a powder coating process.

11. The method according to any one of claims 1 to 10, further comprising a step of cleaning the steel part prior to coating, preferably selected from washing, annealing, degreasing, pickling or a combination thereof.

12. The method according to any one of claims 1 to 11, wherein the adhesion promoter layer is applied in a layer thickness of 25 μm or less, preferably 0.01-20 μm, more preferably 0.05-15 μm, still more preferably 0.1-10 μm.

13. The method according to any one of claims 1 to 12, wherein the enamel layer is applied in a layer thickness of 1mm or less, preferably 1-500 μm, more preferably 5-250 μm, more preferably 10-180 μm, wherein the layer thickness is measured on a cross-sectional abrasive sheet with a microscope.

14. Enamelled steel part obtainable by a method according to any one of claims 1 to 13.

15. Use of an enamelled steel part according to claim 14 in kitchen appliances, preferably ovens, in particular as a baking tube, baking tray or mould, and as an accessory in or on a cooking chamber, such as a hot air guide plate, a grill grid, a baking string, a baking tray receiving grid, a telescopic guide rail, a steam bar and/or an air discharge plate.